1. Field of the Invention
The present invention pertains to a zoom lens system, and more particularly, to a zoom lens system suitable for the photo-taking optical system of a digital camera or lens shutter camera.
2. Background of the Invention
Various types of zoom lens systems for use in a digital camera or lens shutter camera have conventionally been proposed that comprise, from the object side, a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power and a fourth lens unit having positive optical power.
However, in these conventional zoom lens systems, the focal length in the shortest focal length condition is around 40 mm if converted into a camera using 35 mm film. These zoom lens systems are therefore unsatisfactory for a user desiring a shorter focal length.
In addition, the need has increased in recent years for zoom lens systems for digital and lens shutter cameras that permit photo-taking of an object at close distance, and among the zoom lens systems having the optical power arrangement described above, a zoom lens system capable of macro-photography has been proposed (Japanese Published Patent Application 5-76009).
However, the zoom lens system disclosed in said patent application has a construction in which the lens units move along the optical axis in a complex manner for the purposes of photo-taking of an object at close distance (hereinafter macro-focusing) and changing the magnification. Therefore, it is necessary to manufacture the lens barrel with high precision. If the lens barrel is not manufactured with sufficiently high precision, the lens units would become decentered while moving for macro-focusing or zooming, which would lead to a marked deterioration of the image.